Parametric Study of Unsteady-State Flow Modulation in Trickle-Bed Reactors

Unsteady-State Liquid Flow Modulation (Periodic Operation) Was Investigated for Hydrogenation of Alpha-Methylstyrene to Cumene in a Hexane Solvent over 0.5% Pd on Alumina Spheres. This Test Reaction Was Run under Both Gas and Liquid Reactant-Limited Conditions. It is Shown that Periodic Liquid Flow Modulation Can Alter the Supply of Liquid and Gaseous Reactants to the Catalyst and Result in Reactor Performance Different from that Obtained under Steady-State Conditions. the Effect of Key Parameters Such as Extent of Gas/liquid Limitation, Total Cycle Period, Cycle Split, and Liquid Mass Velocity Were Investigated Experimentally to Demonstrate the Cause-Effect Relationships in Periodic Operation. Performance Enhancement Was Observed for a Wide Range of Operating Conditions under Gas Reactant Limitation. It Was Strongly Dependent Upon the Extent of Catalyst Wetting under Liquid-Limited Conditions. the Feasibility of Achieving Improved Reactor Performance is Shown to Depend on the Extent of Reactant Limitation, the Cycle Period and Split, Mean Liquid Mass Velocity, and the Improvement of Liquid Maldistribution by Periodic Operation. Moreover, Performance Enhancement is Dependent Upon the Induced Flow Modulation Frequency and This is Discussed in Relation to the Natural Frequency of the Governing Process

Multicomponent Flow-Transport-Reaction Modeling of Trickle Bed Reactors: Application to Unsteady State Liquid Flow Modulation

A One-Dimensional Reactor and Catalyst Pellet Scale Flow-Transport-Reaction Model Utilizing the Multicomponent Stefan-Maxwell Formulation for Inter- and Intraphase Transport is Developed to Simulate Unsteady State Operation in Trickle Bed Reactors. the Governing Equations and Method of Solution Are Discussed. Results Are Presented for a Model Reaction System (Hydrogenation of A-Methylstyrene) under Gas Reactant Limiting Conditions, for Liquid Flow Modulation as a Test Case of Unsteady State Operation. Model Simulations Predict that Periodic Liquid Flow Modulation Can Alter the Supply of Liquid and Gaseous Reactants to the Catalyst and Result in Reactor Performance Enhancement above that Achieved in Steady State Operation. the Effects of Key Modulation Parameters Such as the Total Cycle Period, Cycle Split, and Liquid Mass Velocity Are Simulated, and Model Predictions Are Found to Be in Agreement with Experimentally Observed Trends in the Literature. © 2005 American Chemical Society

Comparison of Upflow and Downflow Two-Phase Flow Packed-Bed Reactors with and Without Fines: Experimental Observations

This Study Compares the Performance of Laboratory Trickle-Bed and Upflow Reactors over a Range of Operating Conditions, using the Hydrogenation of Α-Methylstyrene to Cumene in Hexane Solvent over 2.5% Pd on Alumina Extrudate Catalyst as a Test Reaction. It is Shown that the Trickle Bed Performs Better Than the Upflow Reactor at Low Pressures When the Reaction is Gas Limited, Due to Ready Access of the Gas to the Incompletely Externally Wetted Catalyst, While the Upflow Reactor Performs Better at High Pressures When the Liquid Reactant Limitation Controls the Rate, Due to the Completely Wetted Catalyst. Comparison of the Two Reactors at Different Pressures, Liquid Reactant Feed Concentrations, and Gas Flow Rates is Presented, and Differences in Performance Are Explained based on the Observed Shift from Gas Limitation to Liquid Limitation. Experiments in Beds Diluted with Fines Yield Identical Performances in Both Upflow and Downflow Modes of Operation under Both Gas- and Liquid-Limited Conditions, Corroborating the Fact that Hydrodynamics and Kinetics Can Be Decoupled by using Fines. It is Also Shown that the Advantage of Upflow or Downflow Depends on Whether Liquid or Gas Reactant is Rate Limiting and that a Single Criterion for Identifying the Limiting Reactant Can Explain Most of the Data Reported in the Literature on These Two Modes of Operation

Evaluation of Trickle Bed Reactor Models for a Liquid Limited Reaction

The Isothermal Decomposition of Hydrogen Peroxide on a CuCr Catalyst in a Laboratory Scale Trickle Bed Reactor Was Used to Test Model Predictions of the Dependence of Liquid Reactant Conversion on Space Time for Different Operating Conditions. It is Assured that the Decomposition of Hydrogen Peroxide is a First Order Liquid-Limited Reaction. Comparison of Model Predictions and Experimental Data Indicates that Both External Mass Transfer Effects and Incomplete External Catalyst Wetting Need to Be Accounted For. Dudukovic\u27s (1977) Approximate Model for the Catalyst Effectiveness Factor Adequately Simulates Both Effects

Single Phase Flow Modeling in Packed Beds: Discrete Cell Approach Revisited

A Discrete Cell Model (DCM), based on the Minimization of the Total Rate of Energy Dissipation, is Applied to Compute the Fluid Velocity Field in Two-Dimensional Packed Beds. the Analysis of the Individual Terms of the Energy Dissipation Rate Equation is Also Presented. the Results Obtained by DCM Are Validated Both by Comparing Them with the Solutions of Ensemble-Averaged Momentum and Mass Conservation Equations (CFDLIB Code) and by Available Experimental Results. the Differences between DCM and CFD Simulations Were Found to Be Confined to within a 10% Band over a Wide Range of Reynolds Numbers (Re\u27 = 5-171). Thus, a Reasonable Agreement between the Predictions of the Two Methods Can Be Claimed for Engineering Applications. an Acceptable Agreement of DCM/CFD Predictions and the Available Experimental Data in the Literature is Also Achieved. the Presented Case Studies Justify the Use of DCM for Predicting the Fluid Velocity Fields in Packed Beds with Complex Internal Structures and with Irregular Distributed Gas Feeding Points. (C) 2000 Elsevier Science Ltd. All Rights Reserved

Prediction of Pressure Drop and Liquid Holdup in High-Pressure Trickle-Bed Reactors

The Holub Et Al. (1992, 1993) Phenomenological Model for Pressure Drop and Liquid Holdup in Trickle Flow Regime at Atmospheric Pressure Was Noted by Al-Dahhan and Duduković (1994) to Systematically Underpredict Pressure Drop at High Pressure and High Gas Flow Rates. in This Study, the Holub Et Al. (1992, 1993) Model Has Been Extended to Account for the Interaction between the Gas and Liquid Phases by Incorporating the Velocity and the Shear Slip Factors between the Phases. as a Result, the Prediction of Pressure Drop at the Operating Conditions of Industrial Interest (High Pressure) Has Been Improved Noticeably Without Any Significant Loss in Predictability of Liquid Holdup. the Extended Model and the Comparison between its Prediction and Experimental High Pressure and High Gas Flow Rate Data Are Presented and Discussed

Two-Phase Flow Distribution in 2D Trickle-Bed Reactors

An Extended Discrete Cell Model (DCM), based on Minimization of Energy Dissipation Rate, is Applied to Predict Two-Phase Flow Distribution in the Two-Dimensional Trickle-Bed Reactors. the Main Advantages of DCM Are that It Can Qualitatively Capture the Experimental Observations, and Readily Distinguish between Flow Distribution in Prewetted and Non-Prewetted Beds, as Well as Reflect the Effects of Bed Structure and Inlet Liquid Distributor on Two Phase Flow Distribution. for Comparison Purpose, the Results of Liquid Distribution Obtained by DCM Are Compared with Both Computational Fluid Dynamics (CFD) Simulations and Experimental Observations in a 2D Bed. the Achieved Qualitative and Quantitative Agreement Justifies the Use of DCM in Predicting Two Phase Flow Distribution in Packed Beds. a Particle Wetting Factor (F) Has Been Introduced into DCM to Account for the Influence of Particle Surface Wetting on Liquid Flow Distribution. Analysis of DCM Simulations Presented based on Maldistribution Factor (Mf) Provides a Convenient Way of Quantifying the Effects of Particle Surface Wetting, Distributor Design and Bed Depth on the Two-Phase Flow Field

CFD of Multiphase Flow in Packed-Bed Reactors: II. Results and Applications

Numerical Simulations of Multiphase Flow using the K-Fluid CFD Model Described in Part I of This Issue Are Presented for Packed Beds at Various Operating Conditions. Both Steady-State and Unsteady-State (E.g., Periodic Operation) Feed Conditions Were Studied Numerically. Predictions of the K-Fluid CFD Model Are Comparable with the Experimental Data in the Literature for Liquid Upflow in a Cylindrical Packed Bed. in Addition to the Mean Porosity and the Longitudinally Averaged Radial Porosity Profile, the Variance of the Porosity Distribution is Needed for Predicting the Probability Density Function of the Sectional Flow Velocity. in the Trickling Flow Regime, the K-Fluid CFD Model Provides Reasonable Predictions of the Global Liquid Saturation and the Pressure Gradient. Relevant Applications of the K-Fluid CFD Model Are Identified in Quantifying the Relationship between Bed Structure and Flow Distribution in Various-Scale Packed Beds. the Combined Flow-Reaction Modeling Scheme is Proposed through the Mixing-Cell Network Concept, in Which the K-Fluid CFD Simulation Can Provide the Information on Sectional Flow Distribution

Comparison of Trickle-Bed and Upflow Reactor Performance at High Pressure: Model Predictions and Experimental Observations

Comparison of Laboratory Trickle-Bed and Up-Flow Reactors over a Range of Operating Conditions, Which Cover Both Gas and Liquid Reactant Limitations, Has Been Investigated using Hydrogenation of Alpha-Methylstyrene to Cumene in a Hexane Solvent over 2.5% Pd on Alumina Extrudate Catalyst as a Test Reaction. the Results Show that When the Reaction is Gas Limited at Low Pressure and High Liquid Feed Concentration, Trickle Bed Reactor Outperforms the Upflow Reactor. at High Pressure and Low Liquid Feed Concentration, the Reaction Becomes Liquid Limited and Upflow Reactor Performs Better. It is Concluded that the Advantage of Upflow or Downflow Depends on the Reaction System Type (I.e. Whether the Reaction is Liquid or Gas Limited). a Single Criterion for Identifying the Limiting Reactant is Proposed Which Can Explain Most of the Data Reported in the Literature on These Reactors. Comparison of the Experimental Observations and the Predictions of the Reactor Scale and Pellet Scale Models Available in the Literature is Presented

Investigation of a Complex Reaction Network: I. Experiments in a High-Pressure Trickle-Bed Reactor

A High-Pressure Trickle-Bed Reactor Was Used to Achieve High Productivity and Selectivity for the Manufacture of a Key Herbicide Intermediate (Α-Aminomethyl-2-Furanmethanol (Amino Alcohol, AA) from Α-Nitromethyl-2-Furanmethanol (Nitro Alcohol, NA). Raney Nickel Catalysts of Varying Activity Were Prescreened for Suitability in Trickle-Bed Operation. the Effect of Operating Parameters Such as Reactant Feed Concentration, Liquid Mass Velocity, and Temperature on the Yield of Amino Alcohol (AA) for RNi-A Are Discussed. the Superiority of Trickle-Bed Reactors over Others Such as Semibatch and Batch Slurry Systems is Demonstrated. the AA Yield Increases with Decrease in Feed Reactant Concentration and Liquid Mass Velocity, as Well as with Lowering of the Operating Temperature. a Maximum Product Yield of 90.1% Was Obtained at 8.3 Wt. % Feed Concentration of Nitroalcohol (NA), While at the Highest Feed Concentration of 40 Wt. % NA, the Maximum Product Yield Was 58%. the Volumetric Productivity of AA Was Significantly Higher at Higher Reactant Feed Concentrations, Even Though the Yield Was Lower under These Conditions. the Operating Temperature Was Also an Important Parameter, with a Lower Temperature Being Preferable for Trickle-Bed Experiments. Bed Dilution with Inert Fines Improved Catalyst Utilization and Increased the AA Yield and Productivity in the Laboratory-Scale Trickle-Bed Reactor